Free transfers is a reality that is slowly fading away from football for top players, players who enter their last year of contract are generally sold by their clubs if they see a chance that the player will not renew his contract. It is hard to argue it is not prudent on part of the club. It is better to cash out, rather than have a de-motivated player turning up to play which can impact the morale of the other players negatively too.
We look at the last 5 free transfers in the Wenger era (who made at least 10 appearances, so no Mart Poom, Daniel Karbassiyoon or Sebastian Svärd are included in this list) and how they have turned out for the club.

Mathieu Flamini (2004, 2013)
Arsenal actually signed Flamini twice on a free transfer in 2004 from Marseille and in 2013 from AC Milan, in his 2 stints combined he turned out 242 times for the Gunners scoring 13 goals. Towards the end of his first spell in 2008, he was part of a formidable midfield with Fabregas and Hleb, so it was a negative to see him leave for a free to AC Milan. Defensively, Flamini may not have had the physical presence that a Granit Xhaka now provides to the midfield but what he had was abundance of energy and enthusiasm, perhaps a bit much. During his second spell, he tended to pick up a yellow card the moment he was on the pitch and was walking a tight rope from there on, putting the team in a bit of jeopardy. He picked up 42 yellow cards in the 2 spells combined and but surprisingly only got sent off once.
Highlight of his time at Arsenal remains the long range goal against Newcastle during his first stint, which was so unlike him and the brace in League Cup against Tottenham.
Verdict : Flamini cannot be regarding as a failure for Arsenal, he always did the job for the team and while not a superstar he was an essential cog of the team

Yaya Sanogo (2013)
Arriving relatively unknown from AJ Auxerre, Yaya Sanogo failed to generate any type of first team worthy performances, the return of 1 goal in 20 games for the club typifies the same. His solitary goal came in a Champions League win to Borussia Dortmund in a winning effort. Other than that, there is not much to write about his Arsenal career. Briefly, he threatened to become a cult figure with the "No Sanogo, no party" craze in the summer of 2014, but that was about it. Probably the only highlight he would be remembered for in Arsenal shirt will be his 4 goals in 22 minutes against Benefica in the Emirates Cup where he scored one of his goals with a back-heel too.
Verdict : Sanogo's Arsenal career never really took off in the 4 years at the club with multiple loan stints also failing to launch his career. He has now parted ways with Arsenal. Fair to say Arsenal are better off now.

Marouane Chamakh (2010)
Arriving in the summer of 2010, apparently to fill in Emmanuel Adebayor's shoes one year after his departure to Manchester City in 2009, Chamakh began his career brightly at Arsenal before quickly fading out. He was never going to be a first choice striker against a fit Robin Van Persie. His debut season saw him score 11 goals in 44 outings, which is a low number to be a first choice striker. The 2011-12 season saw him score just 1 goal in 19 outings. The highlight of his time was surely the crazy 7-5 match at Reading in the League cup, which saw him score an outrageous long distance chip over the goal keeper and also confirm the victory with his second goal.
Verdict : Chamakh could never establish himself as a first choice striker or score a decent number of goals for the team. His signing was not one the best piece of business by Arsene Wenger.

Sol Campbell (2001, 2010)
Ooh where to start, if there ever was a sweet victory scored over Tottenham by Arsenal, the signing of Sol Campbell on a free from them has to be the sweetest. Moving between the North London rivals was a brave move on Campbell's part but then he was a brave man. One of the England's finest of his generation, he went onto become the cornerstone of success for Wenger's sides and was also an important cog of the Invincibles of 2004. He is also the only Arsenal player to score in a Champions League final, giving the 10 man Arsenal the lead against Barcelona in Paris in 2006. He returned again to the club in 2010 as a stop gap measure to cover for injuries to William Gallas and Thomas Vermaelen but was past his prime by then.
Verdict : Sol Campbell represents the best piece of free business done by Arsene Wenger during his reign. If Kolasinac can emulate Campbell's effect and success with the team, what a signing he could be.

Sylvinho (1999)
Signed from Corinthians in 1999, Sylvinho is the last left back before Kolasinac which was signed on a free by Wenger. He was also the first ever Brazilian to play for the club. Replacing the aged Nigel Winterburn, he was quickly replaced himself by the prodigy that was Ashley Cole. Won many admirers during his time at the club due his long range screamers, was included in 2000-01 Premier League team of the season too.
Verdict : Sylvinho was a good signing for Arsenal even if he did not have a long career with Arsenal. There are many similarities to be found between Kolasinac and Sylvinho other than the obvious one of both of them being Left backs. Both are also first players of their respective countries to be signed by the club.

Sead Kolasinac is coming off a strong season at Schalke and Arsenal have done good to get him on a free and wrap up the deal early, giving him time to ease himself into the squad. Over the years, free signings who have actually gone on to play for the club have been moderate performers save for Sol Campbell, can Kolasinac buck that trend ?