What can Arsenal expect from Nuno Tavares?

'Why are they signing another left-back?!'

That was the question reverberating around the Twittersphere on Saturday evening when Arsenal announced the signing of Benfica left-back Nuno Tavares.

I mean, they already have the second-best left-back in the Premier League in Kieran Tierney, who is himself still young enough that Arsenal won't have to think about replacing him for another decade. So why are they signing another one?

It's a reasonable question, but those asking it are underestimating the importance of the humble understudy.

In modern football, you need two players for every position. The growing scheduling demands mean that even those who aren't playing in Europe need to be well covered, and that's especially true in specialist positions like left-back.

It's not as if he's there to polish boots and warm the bench, however. Tierney will start more often than not, but there's no hiding from his blotchy injury record. His inability to play 50+ games a season has led to Granit Xhaka and Bukayo Saka being dragged out of position to do the graveyard shift in recent years, so signing specialised backup was the logical solution.

Arsenal have done that on the cheap, while still landing themselves a quality player whose best years lie ahead.

Tavares will benefit from working with Tierney, learning his trade from one of the best professionals around, but he also brings something different to the table.

He differs from the Scot in that he is rough around the edges and far from the finished article defensively. But he is stronger, quicker, and just as good at crossing, which could mean that he is occasionally the preferred option.

He was never first-choice at Benfica, never unable to unseat Grimaldo for a sustained period of games. But he racked up plenty of minutes, 1,302 last season, mostly against teams lower in the division when they came up against a rigid low block.

On the ball, he's the perfect transitional full-back, and there will be moments in the season where Arsenal are better for having Tavares on the pitch than their usual Scottish starter.

There may even be times where both of them at once is the way to go. Mikel Arteta likes to mix his tactics up now and again, and having two left-backs - one of which is well capable of dropping into a back three - means he can switch to 3-4-3 or 3-5-2 without playing anyone out of position.

It may seem like a strange signing at face value - particularly at a time when Arsenal desperately need reinforcements in various other areas of the park. But his presence in the squad eases the burden on Tierney, and gives Arteta another tool to play with as he seeks to rebuild Arsenal into a side capable of mixing it at the top of English football again.

Logical transfer business. It will never catch on.