I know Biden thinks he can work with Republicans.
A Republican majority remaining in charge of the senate will be an obstacle to anything Biden wants to do, not just a 'check'
Look at the bills he democratic majority in the House has passed that died when sent to the senate.
If you want bills that raise the minimum wage, protect your right to vote, protect your vote, get control of covid, provide help to victims of covid, etc..... you're going to NEED democrats having majorities in both chambers and in the White House.