I'm surprised that no one has responded to your question yet. In fact there is very little about SalesLoft in the Community discussions except a couple that Josh Hill has responded to with the overall message being that they don't integrate with Marketo, so you loose the ability to track clicks and opens.
In August 2017, our sales team trialed Outreach, although I was concerned since MSI could do 80%+ of what they wanted Outreach to do. Outreach created SFDC tasks that always had the prefix [Outreach] [Email] on the subject and then had [Out] or [Opened], so we were able to use that in Marketo for suppressing sending batch emails to persons being sent Sales Emails in a certain timeframe. Arguably easier than juggling SFDC campaign memberships. Ultimately, they decided it was too cumbersome and MSI gave them the basic capability they need to send and track their performance.
During this time, Sales was using DialSource to queue up their call plans, but that wasn't working well for them. So when our DialSource agreement expired in February, Sales decided to get a sales automation tool with a built in dialer - SalesLoft. It creates SFDC tasks that always have the prefix 'Email:', but that is all, so you can't tell if the email has been opened or clicked outside of SalesLoft.
As Josh noted, during the Outreach trial, we saw an increase in our corporate emails not being delivered and either bouncing or going into spam folders because each salesperson sent a thousand emails a day (Outreach maximum). Now we have twice as many salespersons and I'm even more concerned that our spam bounces will continue to increase. I'm trying to convince leadership that only customized emails should be 'Lofted' to highly qualified prospects and not use SalesLoft to bulk send emails - hope I'm successful. If they do that, we won't need email click info in Marketo for scoring and triggering alerts because Sales will be well aware of the handful of top prospects they're engaging with and won't need that.
There is a lot of alignment of systems and people that need to happen to make these email tools play nicely. Unfortunately, sales usually just wants control to do it themselves even though MSi and Marketing can do a better scalable job for mass prospecting and nurture. I would prefer to see these tools used for post MQL communications or Call Down Only lists when you can't email a person.