The all volunteer army is more efficient and more professional than a conscripted army. However, in the recent wars, only 1% of the population fought in those wars, so while just 1% of the population fought in those recent wars, back in America there was a sense as if there were not wars going on at all. So, the dark side of having an all volunteer army is that the sacrafices are disproportionately shouldered by just 1% of the population. For example a guy in my unit was going on his 7th combat tour. In another case an army ranger was on his 15th combat tour before he was finally killed in action. He started his 1st combat tour in 2001 shortly after 9/11.
On the other hand, some of the cool things I saw were guys with missing limbs that they lost on one combat tour and they would recover, get a prosethitic limb and then volunteer for another combat deployment and go on a combat deployment with one leg and a fake limb. They got mad respect even from the Afghans. We had a few cases like that. We even had a double amputee go back to war. For us, it was about defending the homeland from another 9/11 terrorist attack. Here is an article that discusses this phenomon with my country's army:http://www.nbcnews.com/id/39356718/ns/w ... ghanistan/https://taskandpurpose.com/boston-green ... e-injuries
The Afghans even gave a nickname to one of our one legged soldiers "The One-Legged Warrior of Ashaque."https://www.npr.org/templates/story/sto ... 1478247770
So the advantage of the all volunteer army is that you have soldiers who want to be there and who fight with heart and are more professional. The disadvantage though is that sacrifice is not shared by the nation so the effects and sacrifice of the war is not felt by the entire nation aside from those taxpayers who pay for the war, they will feel the financial cost but not the full brunt of the true sacrifice.
In the past with conscripted armies, they were not as efficient or professional, plus soldiers did not always fight with heart because they didn't want to be there, but the cost of these conscripted armies might have been lower though I can't say for sure because I don't have data to back that up. I would imagine that all volunteer armies could be more expensive. There is trade offs to everything. With conscripted armies you have more shared sacrifice and more of the nation is feeling the full brunt of the sacrafice like they did in World War II for example.
The conscripted army gives the entire nation a greater respect and appreciation for the horrors of war and makes it more likely that the population will question the need to go to war given that it has developed a great respect and appreciation for the horrors of war plus the astronomical financial cost involved in going to war too. Governments will be less likely to quickly rush into war when the population asks more questions and demands good reasons for going to war when they know it's going to be their neck and life on the line.