Most of a Keynote deck converts cleanly: text, shapes, photos and speaker notes. The trouble is always in a few specific places. We audit each slide before converting and tell you exactly which ones to check in PowerPoint.
Keynote's themes use Mac fonts like Helvetica Neue and Avenir. Windows swaps in whatever it has, and the new font is usually wider, so text that fitted spills out of its box. Pick a font to see what the PC will do.
PowerPoint has its own set of transitions and builds. Where there's a close match we use it; where there isn't, the effect falls back to a simple fade so the talk still flows.
If nobody needs to change the slides, a fixed format avoids every problem above.