Before I begin; if you haven't read this detailed article on using the Activity Wizard, it may be useful to give it a glance over:
What are Business Groups?
As explained in the above article, in step 3 of 4 you have an option to add Business Groups to the Activity.
When you add a Business Group you are not Tagging this Activity, only adding the Businesses with the Tag.
Business Groups are actually the Tags that Businesses have previously been added to. It only selects the Businesses within that Tag.
For example; if you have a Tag called 'Restaurants', you may have added all the restaurants in your area to this Tag. When you select the Restaurants Tag, all the Businesses will then be automatically added to the Activity. This saves you time of having to individually search for each Business.
Another example would be for patrols, you may want to add several Businesses to this Activity. You might have a Tag for several streets that Businesses have been added to, for example; 'High Street', If you add this Business Group, all the Businesses that have been Tagged as on the High Street will be added to the Activity.
Pro tip: You can add multiple Business Groups but it may be worth revising what Tags you have so you can really utilise them so they work well for the the mobile teams.
Tagging the Activity
In step 4 of 4 in the Activity Wizard you have the option to now Tag the actual Activity.
This is completely different to adding Business Groups as it does not add any Businesses to the Activity but just simply adds whatever Tags you want to the Activity. Again, you can add as many Tags as necessary that are relevant to the Activity.