Sealer is only of benefit if the tile is in poor condition. Even then I wonder how much benefit... The main problem with sealer is it is a pain in the ass to remove completely. Sealer is a semi-permanant coating that fills in the low spots and allows your finish to spread evenly. Most floor finishes today level well and are self sealing. This makes most VCT sealers more headache than they're worth in most cases.
That said sealer can improve the look of a worn/damaged floor and one cost of sealer could save a few coats of finish if you're trying to build the same level of gloss. Sealer is a semi-permanant coating that fills in the low spots and allows your finish to spread evenly.That said, you still need a minimum of 3 coats of most floor finishs.
Anyway, if you lay your first coat and want the subsequent coats to level better ( a great way to avoid stripping sealer at a later date)... Let it dry completely & BURNISH THE SNOT OUT OF IT. This will give a nice smooth surface for the next coat to level on & builds the shine from the bottom up.