Does tempDB disk perf matter if you have plenty of unused memory?
Even if you have plenty of DRAM, tempdb may still be used.

This happens in a few situations:

Snapshot isolation: Using this feature can create a lot of tempdb activity.

Hash and sort Spills: When the optimiser creates a query plan, it will try to estimate the total amount of memory it needs to run the query. Before the query runs, the estimated memory is allocated. If it turns out (for example, due to bad statistics) that the allocated memory is too small, then SQL Server will spill operators like hash tables and sort buffers to tempdb, EVEN if there is enough memory after the query has started to satisfy the requirement.

Or course, if your queries are perfectly tuned and you run without snapshot isolation, you can avoid these effects. But in most situations, some amount of tempdb activity is to be expected, even on a large DRAM system.