Yes, it does matter. The president will nominate supreme court justices (this president probably several) and those justices hold great power in determination of the legality of our laws.

Yes, it does matter. A republican president with a republican leaning congress can reverse important legislation and push through a conservative agenda that harm citizens since the president would obviously not be using his power of veto against his allies in congress.

We have a 3 branch system of government to keep each branch in check, but when all three branches are dominated by the same party, there is an inherent imbalance in the system.