I'm going to cheat here a little bit and just quote our own match report from Saturday's 3-1 win over Manchester City. And that's not just because Graham's the second best-looking writer on this site.
Fabregas is hardly an all-around midfield giant. His positioning is erratic, his pace is plummeting rapidly into non-existence and he sometimes forgets to defend entirely. It's impossible to assess Fabregas's game without looking at his weaknesses, but it's also foolish to ignore the strengths: he is the best long passer in the Premier League. Few have his vision, few can match the speed of his release and absolutely nobody can drop those raking balls into space as accurately as Fabregas at his best.
Due to the nature of these sorts of highlight videos, we see mostly the latter things, the things that Cesc is really good at. The team-leading (and match-leading!) 90% pass completion, second-most touches, the key passes, a few tackles, and of course the trademark long balls (though he's no longer alone in the squad in being able to provide them — David Luiz obviously, but even Marcos Alonso are quite good at them as well). We don't see his (good or bad) positioning, his anticipation in/out of possession, work rate (or lack thereof), or how the rest of the team balances or unbalances itself around him.
But credit where credit's due, Fàbregas's vision got us a crucial goal and the coach's gamble to start him instead of a more defensive replacement for Matić — or, say, switching to a three-man midfield — paid off handsomely with the three points. Conte was obviously happy with Cesc's contribution, though his post-match comments basically echoed what he's been saying all along about the man who was making just his second league start all season.
"I'm pleased for Cesc above all because this game wasn't easy for him. The last game he played for Chelsea in the line-up was against Arsenal, and then he had an injury. He recovered and I'm very happy for his performance."
"He must continue to improve. For me to have more options is good. It's important to have the whole squad available."
-Antonio Conte; source: Chelsea FC
Presumably Matić, who missed Saturday's game with a minor muscle injury, will be back next weekend against West Brom and Cesc will be back on the bench. Whatever the future may hold for Fàbregas — transfer rumors are being denied at almost the same pace as they are being created — he's undoubtedly a great asset to have in the team ... just maybe not as a full-time starter anymore.