If you are migrating from SharePoint 2007 or your shared drive, remember that you will have to deal with significant differences in the user experience that will affect your user adoption process.
Migrating from SharePoint 2007 or a shared drive will probably require some training and a potentially longer adjustment period. SharePoint users report feeling more productive.
How will third party product dependencies migrate and integrate with SharePoint Online?
Some data and migration systems only offer full functionality when paired with certain browsers. Browser compatibility can be both costly and challenging to maintain over time when not upgraded.