If your distribution list is small then your normal email program is probably quite adequate. Problems arise when the distribution list becomes large.
Some email programs stop when they encounter the first invalid address. Restarting the sending after correcting or removing the offending address without sending duplicate emails to some recipients is awkward if your list has 20 recipients but is a real nightmare if it has many hundreds of recipients!
Restarting after a power outage has the same or worse problems.
Many ISPs impose limitations on the number of emails that can be sent in a session or in some time period. Sending 800 emails in batches of 50 ten minutes apart would be a real headache with normal email programs, but specialised bulk emailers have extra smarts to send emails in a way that fits in with the ISP's restrictions.