NinjaTrader offers three choices when deciding how often your indicator should be updated. "On bar close" is the default, which uses the least amount of CPU of the three, as the indicator is only updated at the close of each bar. This update occurs just as the bar is becoming the first bar in the history. This would be appropriate for indicators that don't update intrabar, or if you're not interested in seeing the indicator's values on the current bar. However, if you use this on an indicator such as MQ Trender Pro 2.0, the indicator's colors will almost never appear on the current bar as it waits until the bar closes to show the indicator's colors.
The other two choices are "On each tick" and "On price change". These choices are used when you do want to see updates to an indicator intrabar - that is, while the bar is building. The difference between these two is probably insignificant, as a tick generally indicates a price change. It's possible that there can be redundant ticks at times. In most cases, using "On price change" makes the most sense for intrabar use, as most indicators won't change unless price changes. Note that "On price change" does update at the close of each bar, even if price hasn't changed.
The advantage of using NinjaTrader's default "on bar close" setting is that it only uses CPU at the close of each bar. If you do want to see an indicator's updated value while the bar is building, using "On price change" will make sure the indicator updates intrabar if price changes. This may be the best setting for intrabar updates for most traders.
You can find even more details on this setting at this link: