I was told a coat of primer will make old paint curl and loosen even more than it is now. Therefore making scraping and sanding more complete.
Yes and no, mostly no. An acrylic primer, just like the paint, is elastic or stretchy. This can over time cause old hard, cracked oil based paints to loosen and peel. Generally this process can take 2-3 years or more.
At the same time a primer can glue down loose edges of peeling paint. Making removal very difficult or impossible.
It is best to do the best preparation possible before priming. If any additional loose paint become apparent after priming you will need to deal with it before applying paint.