It is still best to have an account at both places. Here are a few reasons I can think of:
1. Skybook posts lines later than Pinnacle. So by the time Skybook has lines up, you may have already missed out on a half point move (or more).
2. The half point is not always worth what it seems. It is not really worth an extra -110. More like -106. And in some cases where an NCAAB line is already high like -16 1/2, getting it at -16 doesn't mean a whole lot.
3. Wager limit on the free half point at Skybook is only $300. Pinnacle has higher limits.
4. Skybook adjusts juice on its number quite a bit sometimes. Easily sometimes -116/+104, etc. This can sometimes work out to your favor, but it basically forces you into buying a half point on the juiced up side sometimes. Pinnacle does this also, but with only -105 juice the comebacks have less of a differential.
I am not knocking Skybook here, but just saying do not limit yourself to only them. Using both places together, you will generally find a good line (quite frequently, the best line on the board for your bet) at one or the other.