Translations : use services like transifex / crowdin ?

I admit i18n isn't an important matter for me, but it's obvious it provides value to the project.

What would be the benefits, and the migration process if any, of using online services like crowdin or transifex?

More generally, is there anything we can do to improve the translation process in any way, or make translators' task easier ?

Anyone with an idea on the question is welcome here :)