If considering controlled crying, I'd be asking myself some very honest questions about what I was hoping to achieve, what my perception of the process was, and then what my child's perception of the process was likely to be, and finally what unintended consequences the action might have on top of the grand plan of my child learning to sleep alone.
I personally believe the distress of a crying child left alone for 5 minutes, 10 minutes, an hour, is immensely psychologically damaging to them, both in the short and long term.
I also believe the unintended consequences include: long term damage to child's trust in parent and decreasing likelihood of child being able to communicate their needs successfully; blunting of maternal instinct and increasing inability to respond to child's distress and other wants.
Controlled crying may be training your child to sleep alone, but it is also arguably training you to dismiss their cries as "not serious" or "attention seeking" until they are absolutely frantic.
Maybe I'm wrong. But I'd be really interested to see a correlation study comparing parents who leave their children to cry alone and parents who complain that their children tantrum regularly. There seem to be clear links of relationship dynamic to me.
I'd also be interested to see a correlation studying comparing the controlled crying parents with those who complain later that their teens don't communicate with them at all.
And I also think it is worth noting that Richard Ferber, who invented the technique, has since distanced himself from many of the ways people apply it, saying that while it works for some children to be left alone for a couple of minutes and they drop off, he NEVER intended for it to cause hours of distress for anyone.