Before installing a big plugin I'm always scared of the blank page so I usually add define('WP_MEMORY_LIMIT', '64M'); to wp-config.php beforehand. I was thinking I could add it immediately after any WordPress install. Does this have potential downside?
The short answer is no. The long answer is "it is complicated".
The memory limit is there to protect you from malfunctioning code eating all your available memory, something that will make your site less responsive for a while.
(I tried to explain the issues around this setting here)
This setting will not matter if your site doesn't handle a lot of traffic, or if you have a lot of available memory, otherwise you should ask yourself why do you use bloated plugins and look for alternatives.
In any case you should try to set the lowest working limit and not go for 64M without trying lower limits first