So my thoughts re: Email Registration for the 2p its worth. But sure this has been done to death elsewhere…
The advantage is simple - you get the email address so you can do on- boarding / autoresponders / marketing automation to nudge them into the steps required to actually install and/or use your app and ultimately become a paying customer. Also potential for x-selling at later date - despite the insta-twitter-book email lists are valuable.
I really can’t think of many apps (outside of really simple phone type apps) that wouldn’t benefit in some way from on-boarding. (And most of the successful phone apps do ‘in app onboarding’ but you have to get them using the app in the first place for that to work).
The downsides - some users may be reluctant and either give you false/throwaway address or just bounce/abandon. The false/throwaway address doesn’t really cause you problems - nothing lost over no download form. Bounces may cause you problems, but its not the number of bounces you need to be worried about - its the subset of bouncers who would have become customers. And this is hard to test.
So for everyone having a sign up form is sure to reduce the number of downloads, but the unknown is how many of those downloaders you’ve lost were serious prospects.
After resisting a signup form in my own business for a long time I would now have one in just about every circumstance I can think of.
Final thought - you are not your customer. We’re nerds. I am super protective of my email address. I hate spam. I wouldn’t download something that I wasn’t going to try out straight away. I want to read up and try out a product myself. The last thing I want is some salesperson trying to talk to me, and definitely not by phone god dammit! Most people are not nerds. Your customers may not be like you.