Thanks for your question. Without the integration, you will have to download excel files from both Marketo and Gotowebinar to create reports. For example, you would download a list from Marketo of invitees, and then a list out of Gotowebinar of registrants, to find out who still has not registered.
The integration (which is easy to setup, just go to launchpoint in admin and the connection is pretty straightforward), you can monitor by program status who is invited, registered, attended, no show, attended on-demand etc.
Hope this helps.